Method of controlling clutch of continuously variable transmission system

Abstract

A method of controlling a clutch of a continuously variable transmission system which controls a transmission system by either expanding or contracting the width of a channel between a stationary pulley member and an axially movable pulley member to expand or contract the radius of rotation of a belt wound on the pulleys to eventually vary the belt ratio. The continuously variable transmission system includes a controller unit which executes a control operation by feeding actually detected clutch pressure back to an objective clutch pressure, and an oil-pressure circuit which controls oil pressure in response to signals from the controller unit. The control system implements the sequential steps of (a) delivering a variety of signals denoting the status of the driven vehicle to said controller unit, and (b) causing the controller unit to output signals to the oil-pressure circuit when the controller unit identifies the presence of a hold mode before eventually causing the oil-pressure circuit to control the clutch pressure to a predetermined level.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A method of controlling a progressively engageable fluid actuated clutch of a continuously variable transmission which has a plurality of operational modes, including a hold mode, and which is provided in a vehicle having an engine drivingly coupled to said transmission, having a shift selector movable to a plurality of positions including first and second positions each selecting vehicle motion in a common direction and having an accelerator pedal movable to and from a deactuated position, comprising the steps of: causing said transmission to operate in said hold mode in response to a set of predetermined operational conditions, selecting for said hold mode a target clutch pressure as a function of engine speed and shift lever position, and feedback controlling actual fluid pressure for said clutch based on said target pressure in said hold mode. 
     
     
       2. A method of claim 1, including the step of selecting as said set of predetermined operational conditions said shift selector being set to either of said first or second positions when said detected vehicle speed is below a predetermined speed and said accelerator pedal is in said deactuated position. 
     
     
       3. A method of claim 1, including the step of selecting as said set of predetermined operational conditions said shift selector being set to either of said first or second positions when the detected vehicle speed is below a predetermined speed, the engine speed is below a predetermined speed, and said accelerator pedal is spaced from said deactuated position. 
     
     
       4. A method of claim 1, wherein said step of selecting said target pressure is carried out by setting said target pressure to zero when said engine speed is below a first predetermined speed, by linearly increasing said target pressure to a predetermined pressure value as said engine speed is increased from said first predetermined speed to a second predetermined speed, and by maintaining said target pressure substantially at said predetermined pressure value when said engine speed is above said second predetermined speed. 
     
     
       5. A method of claim 4, wherein said predetermined pressure value is respectively a first pressure value and a second pressure value and said first predetermined engine speed is respectively a first speed and a second speed when said shift selector is respectively set to said first position and said second position. 
     
     
       6. A method of claim 1, wherein another of said operational modes is a starting mode, said transmission changing from said holding mode to said starting mode in response to a set of predetermined operational conditions which include said vehicle speed being below a predetermined speed, said accelerator pedal being spaced from said deactuated position, and said engine having a speed above a predetermined speed. 
     
     
       7. A method of controlling a progressively engageable clutch of a continuously variable transmission which has a plurality of operational modes, including a hold mode, and which is provided in a vehicle having a shift selector movable to a plurality of positions which include first and second positions each selecting vehicle motion in a common direction and having an accelerator pedal movable from a deactuated state to an actuated state, comprising the steps of: detecting whether the speed of said vehicle is below a predetermined speed; detecting whether said accelerator pedal is in said deactuated state; detecting whether said shift selector is set to either of said first or second positions; causing said transmission to operate in said hold mode in response to a set of predetermined operational conditions which include said shift selector being set to either of said first or second positions when said detected vehicle speed is below said predetermined speed and said detected accelerator pedal state is said deactuated state; respectively selecting first and second objective levels of clutch engagement when said detected position of said shift selector is respectively said first position and said second position while said transmission is being operated in said hold mode; and controlling said clutch so as to shift an actual level of engagement thereof toward said selected one of said first and second objective levels of engagement when said transmission is being operated in said hold mode; including the step of detecting the speed of an engine of said vehicle; and wherein said step of selecting said first and second objective levels of clutch engagement is carried out by selecting as said first objective level of clutch engagement one of a first plurality of predetermined values corresponding to respective engine speeds and selecting as said second objective level of clutch engagement one of a second plurality of predetermined values corresponding to respective engine speeds. 
     
     
       8. A method as recited in claim 7, wherein said step of controlling said clutch is carried out by varying a fluid control pressure, a progressive increase in said fluid control pressure effecting a progressive increase in a level of actual clutch engagement, said step of selecting said first and second objective levels of clutch engagement being carried out be respectively selecting respective objective pressure values. 
     
     
       9. A method as recited in claim 8, wherein said step of controlling said clutch includes the steps of detecting an actual value of said fluid control pressure and effecting feedback control of said fluid control pressure with respect to said selected objective pressure value and said detected actual value. 
     
     
       10. A method of controlling a progressively engageable clutch of a continuously variable transmission which has a plurality of operational modes, including a hold mode, and which is provided in a vehicle having a shift selector movable to a plurality of positions which include first and second positions each selecting vehicle motion in a common direction and having an accelerator pedal movable from a deactuated state to an actuated state, comprising the steps of: detecting whether the speed of said vehicle is below a predetermined speed; detecting whether said accelerator pedal is in said deactuated state; detecting whether said shift selector is set to either of said first or second positions; causing said transmission to operate in said hold mode in response to a set of predetermined operational conditions which include said shift selector being set to either of said first or second positions when said detected vehicle speed is below said predetermined speed and said detected accelerator pedal state is said deactuated state; respectively selecting first and second objective levels of clutch engagement when said detected position of said shift selector is respectively said first position and said second position while said transmission is being operated in said hold mode; and controlling said clutch so as to shift an actual level of engagement thereof toward said selected one of said first and second objective levels of engagement when said transmission is being operated in said hold mode; and including an alternative set of predetermined operational conditions causing said transmission to operate in said hold mode, said alternative set of conditions including said shift selector being set to one of said first and second positions when said detected vehicle speed is below a predetermined vehicle speed, said detected accelerator pedal state is in said actuated state, and a detected speed of an engine of said vehicle is below a predetermined engine speed. 
     
     
       11. A method as recited in claim 10, wherein said predetermined speed of said engine is approximately 1,000 revolutions per minute and said predetermined speed of said vehicle is approximately 8 kilometers per hour.